The present invention relates to liquid air freshener and insecticidal compositions, particularly those which can be evaporated from a container through a wall such as a membrane.
Air freshener and insecticidal compositions are well-known. These are used to fragrance or deodorize an environment or to control insects. Such compositions have traditionally been in solid form, but now may be in liquid, including thickened liquid or gelled, form. The liquid is generally held in a chamber.
The chamber may have a wicking arrangement such that the composition is evaporated from a wall which is in the form of a porous surface. Alternatively, the chamber may have at least one wall of a material that is permeable to the vapors of the composition, thereby allowing controlled release of the vapors over a period of time. Such an arrangement is described in U.S. Pat. No. 4,534,509, in which the fragrance is enclosed in an impermeable bag with a weak seal along one edge, which prevents escape of the vapors as long as the package is sealed. This is then contained within a larger pouch of a suitable permeable membrane When sufficient pressure is applied by the user, the weak seal ruptures and the volatile composition flows from the inner pouch into the outer permeable pouch, thereby allowing release of the vapors.
An alternative arrangement is described in U.S. Pat. No. 4,634,614 in which the permeable wall is covered with a thin layer of paper coated with a polymer sheet to which adheres a protective sheet which is impermeable to the vapors of the composition. The paper layer tears when subjected to a peeling force such that the protective layer is readily removed and the volatile substance is covered only by a layer of material which is permeable to the vapors, thereby allowing release of the vapors.
A similar arrangement is described in International Patent Publication WO 98/23304 which comprises a membrane laminate having a plurality of layers. The outer layers of the laminate are impermeable to the composition and its vapors, and thus prevent escape of the vapors as long as the package is sealed. Upon opening, delamination occurs at the interface between two selected layers of the laminate, such that the composition is covered only by a layer of the material which is permeable to the vapors of the composition.
In such devices severe constraints are placed on the composition contained within the chamber. In particular, it must be able to evaporate satisfactorily through the wall relatively constantly throughout the life of the device. The device must also be storable for a long time without the composition affecting the properties of the wall or other parts of the chamber. Furthermore, the rate of evaporation of the composition must be controllable by the manufacturer such that a suitable lifetime of the device can be provided, which is generally of the order of about 45 days. It is desirable that after approximately this period, a suitable end of life indicator is provided so that the consumer can see when it is appropriate to buy a new device or refill composition for such a device. Suitable indication means are, for example, a significant visible reduction in the amount of the composition in the device, a change in color of the composition, or a change in form of the composition, for example from a liquid to a non-flowing gel.
In prior art devices of the type in which a composition is always in contact with the wall of a chamber and evaporates out of the chamber through said wall, there is a relatively small amount, for example about 3 g, of the composition present. In order to provide effective fragrancing for a lifetime of about 45 days, the composition must have a high concentration of fragrance with consequently only a small amount of solvent present. The solvent is chosen such as to aid diffusion of the fragrance through the wall of the chamber. A non-polar solvent is generally used since such a solvent has good diffusion properties through such walls.
It is now desired to produce such devices which may contain a greater quantity of liquid composition since some consumers regard this as beneficial. In order to obtain appropriate fragrancing or insecticidal properties under ambient conditions (i.e. at room temperature), it is not possible simply to increase the amount of composition present because this will increase the lifetime of the device. This may not be desirable when a lifetime of about 45 days is required. Furthermore, relatively constant fragrancing throughout the lifetime of device may not be achievable. Additionally, and more importantly, using a larger amount of the composition in the chamber will increase the amount of non-polar solvent present in the chamber. It has been found that such a quantity of non-polar solvent is sufficient to damage the wall during storage or use of the device, which will mean that the device will not function properly once it is opened or has been used for a short time. For example, if the wall is of the laminated membrane type, the membrane may suffer delamination.
It is not possible simply to replace the non-polar solvent with a polar solvent. Polar solvents are known to have poorer evaporation characteristics through membranes, and in particular will not normally pass through membrane walls of the type used in air freshener or insecticidal devices.
It is also desirable that a suitable end-of-life indication be provided for devices of this type so that the consumer can see when it is appropriate to buy a new device or refill composition for such a device. Suitable indication means include the visible absence of any composition in the device. Thus, it is particularly desirable for the composition to be formulated such that no residue of the solvent remains. The end-of-life indication is then simply when all of the solvent of the composition has disappeared, i.e. has evaporated out of the device.